1. Field of the Invention
This invention relates to a muffler for use with a vehicle such as a motorcycle.
2. Description of Background Art
Conventionally, a muffler is attached to an exhaust pipe connected to an engine. In some mufflers of this type, an inner tube having small holes (hereinafter referred to as punching holes) is provided in an outer tube which defines an outer wall, and a sound absorbing material such as glass wool is filled between the outer tube and the inner tube. See, for example, Japanese Patent Laid-Open No. 2007-56714. In such a muffler as just described, a sound pressure of exhaust gas blown out from the punching holes formed in the inner tube is absorbed by the sound absorbing material to achieve sound deadening.
In addition, in the muffler disclosed in Japanese Patent Laid-Open No. 2007-56714, while the punching holes are formed in a similar formation density over the overall inner tube, since the length from an outer circumferential face of the inner tube to an inner circumferential face of the outer tube is not fixed, also the thickness of the filled up sound absorbing material is not fixed. Therefore, non-uniformity occurs with the sound deadening effect by the sound absorbing material such that the sound deadening effect at a thin portion of the sound absorbing material sometimes becomes lower than that at a thick portion of the sound absorbing material, resulting in deterioration of the sound deadening effect. Therefore, it seems possible idea to form the outer tube greater in size than the inner tube in order to assure the thickness of the sound absorbing material. However, in this instance, the muffler becomes too large. Thus, the idea cannot be regarded as a good idea if the actual situation of the demand for reduction in size and weight of a vehicle is taken into consideration.